Heat grill to medium. Season the salmon with 1/2 teaspoon salt and 1/4 teaspoon pepper; arrange on the plank.
Place the plank on the grill and cook, covered, until the salmon is opaque and flakes easily, 12 to 15 minutes.
In a bowl, combine the cucumber, jalapeño, lemon juice, oil, and 1/2 teaspoon salt. Serve with the salmon.